Energy harvesting is a technique that captures energy from an environment in which an energy harvester is placed. Power sources for energy harvesters include electromagnetic sources (e.g., RF signal), kinetic sources (e.g., motion of walking), thermal sources (e.g., temperature gradients), and biochemical sources (e.g., glucose). Kinetic sources are particular attractive because they are readily available. In particular, vibrational sources are relatively common. As such, vibrational energy harvesters such as piezoelectric cantilevers and resonators are especially desirable.
Due to the ability of piezoelectric cantilevers and resonators to withstand large amounts of strain, using them to harvest vibrational energy provides sufficient output for small-scale power applications. The strain can come from many different sources such as human motion, low-frequency seismic vibrations, and acoustic noise and radio frequency (RF) propagations. However, the majority of vibration sources with strong amplitude lie in a range between 4 Hz and 300 Hz with an acceleration of around 1G. Output power depends strongly on the frequency of vibration. Typically, more power is generated at resonant frequencies.
Power harvesting from these electric materials has been investigated for several different potential applications. One such application identified in the prior art pertains to harvesting energy using piezoelectric materials embedded in shoes. Another energy harvesting application involves a piezoelectric polymer backpack strap which generates electrical energy from an oscillating tension in the strap during walking. Even the motion of breathing in and out has been studied for energy harvesting using piezoelectric polymers. Yet another idea has been to use a relatively small windmill to induce vibration in a series of piezoceramic beams. Piezoelectric polymers have also been investigated for generating electrical power from water currents. Another study investigated the storage of electrical energy from energy harvesting devices in batteries and capacitors. Others have characterized various piezoelectric materials, while still others have built wireless self-powered strain sensors that use harvested energy as both power sources and sensing signals. Further still, at least one study has formulated a model of a power harvesting system that comprises a cantilever beam with attached piezoelectric patches. Moreover, others have performed a comparison of piezoelectric, electromagnetic, and electrostatic configurations as a means of harvesting energy from a variety of vibration sources. These studies have generally concluded that the selection of a particular energy harvesting configuration is application dependent, but that piezoelectric materials based harvesters are the simplest to implement overall. What is needed is a vibrational energy harvesting system that can harvest energy from the environment where it is placed.